1. Field of the Invention
The present invention relates to an optical amplifying apparatus, more particularly relates to an optical amplifying apparatus in which the amplification operation is controlled by a computer.
In recent years, there have been remarkable advances made in the technology of optical amplification in research and development of optical communication systems. For example, there has been much more active development of optical cascaded amplifying and repeating transmission systems.
The core of that optical amplification technology is the optical amplifying apparatus. This is utilized as a repeater (in-line amplifier) at a main line side of an optical communication network or as a pre-positioned amplifier (pre-amplifier) or a power amplifier (post-amplifier). At the subscriber side of that optical communication network, it is utilized as a power amplifier (post-amplifier) for compensating for branch loss. Furthermore, viewing the performance of the optical amplifying apparatus, other than the above-described purposes for use in an optical communication network, there has been increased specialization in performance such as use for land-based systems, use for transoceanic systems, and use for wavelength division multiplex (WDM) transmission.
In the future, the focus of development will inevitably shift to the improvement of performance, that is, realization of more sophisticated performance of the optical amplifying apparatus. Realization of such more sophisticated performance will inevitably and naturally require the introduction of computerized control circuits.
The present invention relates to an optical amplifying apparatus into which such computer control has been introduced.
2. Description of the Related Art
Introduction of a computerized optical amplifying control unit enables the performance of the optical amplifying apparatus to be greatly enhanced.
However, a computer-controlled optical amplifying apparatus is subject to new factors of instability which do not occur with conventional optical amplifying control units designed using non-computerized or analog circuits. There are three typical cases of such factors of instability as will be explained in detail below referring to the drawings.
Occurrence of any of the three cases must be of course predicted in computer control. For this reason, it is required to provide the optical amplifying control unit with a failsafe function so as to enable it to cope with any of the above cases which occurs.
However, where such a fail-safe function is provided, there is the problem that the level of the optical output from the optical amplifying apparatus greatly varies or instantaneous disconnection is produced in that optical output. If such a variation or instantaneous disconnection occurs, the main optical signal constituting the important part of the above-described optical output will be instantaneously lost. If such a loss of the main optical signal occurs at the trunk line of the optical communication network, there is a problem in that there might be serious social consequences to the users.